The invention relates to an apparatus and a method for/of combining first and second image data of an object. An ultrasound (US) detector repeatedly generates the first image data of the object and the second image data of the object are generated separately. In the apparatus, means for storing and/or receiving the second image data of the object (such as an image data storage and/or an interface) are provided. For example, the second image data may have been recorded earlier by a computer tomography (CT), a magnetic resonance (MR), a positron emission tomography (PET), an X-ray and/or a three-dimensional (3D) US imaging device. In particular, any 3D image information can be used as the second image data. A combination device combines the first and second image data of the object. The combined image data may be displayed in separate areas of a screen and/or may be superimposed on a screen. More particularly, the invention may be applied in the field of stereographic diagnosis concerning human or animal bodies, but also concerning material research and/or material examination.
Ultrasound detectors are comparatively easy to handle and are able to deliver image information quasi-continuously and, approximately, in real-time. However, in many applications, other imaging technologies (such as the ones mentioned above) provide better results. Therefore, it has been proposed earlier to combine image information of better quality, which has been recorded earlier, with real-time ultrasound image information.
In the scientific publication of Pagoulatos et al.: “Interactive 3-D Registration of Ultrasound and Magnetic Resonance Images Based on a Magnetic Position Sensor”, published in IEEE TRANSACTIONS ON INFORMATION TECHNOLOGY IN BIOMEDICINE, VOL. 3, NO. 4, December 1999, describes an apparatus of the type mentioned above. It is proposed in the publication to use an MR imaging device and to register the imaging object relative to the MR imaging device. The term “register” means that the geometry of the object and the coordinate system of the MR imaging device are brought into a defined relation. The apparatus comprises a position sensor, which is firmly coupled to an ultrasound probe. Using the position sensor and due to the fact that its relative position to the ultrasound probe does not vary, it is possible to track the position and the orientation of the ultrasound probe. However, it is necessary to calibrate the position sensor relative to the ultrasound probe and to register the imaging object relative to the coordinate system of the ultrasound probe. As a result, the MR imaging information and the ultrasound imaging information can be combined.
Using systems of the type described before, it is possible to display MR image information of the same orientation and/or scaled in the same manner as the most recent US image. In other words: it can be simulated that the MR image is recorded in real-time, provided that the image data processing is fast enough.
However, the various calibration and registration procedures are time-consuming and need to be performed with care in order to obtain good results. For example, the position of a set of landmarks on the surface of the object and/or anatomical markers (in case of a human or animal body) is to be detected during registration.
Furthermore, modern US systems enable the user to vary the penetration depth of the US image in the object and/or to change the ultrasound probe. As a consequence, the calibration of the position sensor relative to the ultrasound probe and the registration of the imaging object relative to the coordinate system of the ultrasound probe are no longer valid.
There are prior art ultrasound devices with pre-calibrated pixel sizes wherein the pixel size can be varied by the user. However, only step-like increases or decreases of the pixel size (or of a spatial dimension of the ultrasound image) can be performed with these prior art devices.
U.S. Pat. No. 6,546,279 B1 discloses a method and an arrangement for locating, vectoring and inserting a needle-like medical device toward and into a targeted patient anatomic feature while the patient is being imaged with multi-modality medical imaging equipment. In the second embodiment of the document at least a portion of the patient is imaged with a first imaging technique (such as computed tomography) to provide a first set of imaging data, which has a fixed frame of reference. Ultrasound imaging data is obtained. The ultrasound imaging data is not fixed relative to the fixed frame of reference. Position data is determined for the ultrasound device. Using the determined position data and the ultrasound imaging data, a converted set of imaging data is provided which is referenced to the fixed frame of reference.
The publication “sensor fusion for surgical applications” by Jim Leonhard (15th Annual AESS/IEEE Dayton Section Symposium. Sensing the world: Analog sensors and systems across the spectrum (Cat. No. 98EX178), pages 37-44, XP002253643, New York, N.Y., USA, IEEE, USA) discloses a surgical navigation system which combines preoperate 3d imagery and intra-operate localisation to register a patient.
US 2002/0128550 A1 discloses a diagnostic imaging system. Magnetic resonance image and ultrasound images are registered in a common reference frame.
It is an object of the present invention to provide an apparatus and a method of the type indicated above, which allow lessening the effects of the disadvantages mentioned before, which facilitate the handling by the user and which allow using a greater variety of features of the ultrasound system without loosing time for calibration and/or registration. In particular, it is desirable to adjust the settings of the ultrasound system and/or to change the ultrasound probe and to continue with the ultrasound imaging process without interruption.